Bright cadmium plating



United States Patent BRIGHT CADMIUM PLATING No Drawing. Application November 3 1955 v Serial No. 545,778-

10 Claims. (Cl. 204-50) This invention relates to bright cadmium plating, and

provides an improved process and improved cadmium plating bath for producing bright or brilliant cadmium electrodeposits over a Wide current density range.

We have found that bright and even brilliant ,electrodeposits of cadmium may be formed from a conventional alkali cyanide cadmium plating bath by incorporating in such bath a fraction of a gram per liter of 1a w-aterQdispersible cellulose derivative together with a small amount of an alkylene or polyalkylene glycol or an .alkyl ether derivative of such glycol, Accordingly, the process of this invention for producing bright cadmium deposits comprises electrodepositing cadmium from an aqueous alkaline solution containing from 50 to 150 grains per liter of an alkali metal cyanide, from 10 to 50 grams perliter of cadmium, from fi to gram per liter of a water-dispersible cellulose derivative, and from to grams per liter of a glycolic compound having the for mula in which R a substituent selected from the group coni t ne of h dro en nd a yl a c containing from 1 to 6 carbon atoms, X is a substituent selected from cyanide and of cadmium, and the ratio of cyanide con- I, centration to cadmium concentration, are Within the ranges generally considered optimum in ordinary cadmium l plat n ope a on hu the plati bath vantageously contains from 65 to 130 grams per liter of an alkali metal cyanide and from 15 to 35 grams per liter of cadmium; and generally we prefer to employ from ,6 to A2 gram per liter of the water-dispersible cellulose derivative, together with from 1 to 4 grams per liter of the glycolic compound.

Any cellulose derivative which can be dispersed in the plating bath, i. e. any water-dispersible cellulose derivative, may be employed in carrying out (the method of this invention. We have obtained particularly satisfactory results, however, using .as the cellulose derivative one selected from the group consisting ,of hydror yethyl ,cellulose, carbonymethyl cellulose, and hydroxyethyl carboxymethyl cellulose.-

The glycolic compound used in carrying out the method of the invention is of course a compound of the group consisting of alkylene glycols, polyalkylene glycols, and

alkyl ether derivatives of such glycols. The alkylene and polyalkylene glycols used are preferably those. .in which .the alkyl unit ('i. e. CHX in the general iformula given above) contains from 1 to 3' carbon atoms. "The ya y ne glycols diff r from t e alkyl y n that the former contain a plurality, up to about/5.00, alkyl unit s, whereas the latter contain only one, 'i. e. ;n equals zero in the general formula given above," The alkyl ether derivatives of said glycols preferably are compounds in which the terminal alkyl substituentg i; e. R in the general formula given above, contain 1 -to {6 carbon atoms. lt o llentb i t c dmium electr plat y be deposited from a bath containing only th cellulose derivative and the glycolic compound as addition agents, we have found that it is generally possible to improve the brilliance of the electroplate, and particularly to "broaden the current density range over which br iglit deposits are formed; by incorporating a fraction of a gram per liter of'dissolved nickel in the plating bath. [In er om ,600.0 to g a pe li e of ick y he employed elfectively, but ordinarily we prefer that the amount of nickel incorporated in the bath bein the narrower range from A to /i gram per liter. ,fThe

nickel may be introduced into the bath by dissolving theren a y n kel l wh h is sol le in the at and which does not incorporate an anion having an adverse effect on (the operation of the bath.

A co t alka cyan de Plating ba h, to hich h ab de addi ion a nt may he a e fo making up a plating bath in accordance with this invention customarily is of the following composition:

Ounces per Grams'per Gallon Liter Cadmium (as metal) 2. t) to 4. 5 15 to 35 Sodium Cyanide (total) .5 65-t0 130 Sodium Hydroxideun n, ,3. 2 1 7.5 to 25 Sodium Carbonate 5 0 to A typical alkali cyanide cadmium plating solution is made by dissolving 3.5 ounces per gallon of cadmium oxide and 15.0 ounces per gallon of sodium-cyanide in water. The solution thus formed is rendered alkaline by the caustic soda formed by reaction of cadmium oxide and sodium cyanide in the aqueous solution. A bath, of this basic composition was employed in carrying out the examples of the invention that are summarizedin Tables I to IV below.

Table I below sets forth a considerable number of glycolic addition agents which have been used successfully in the process of this invention. Table I further summarizes the results obtained when an electrodeposit was formed from a solution having the above specified basic composition and containing 0.08 gram per liter of hydroxyethyl cellulose. The electrodeposit was formed in a Hull test cell on sheet steel cathodes, at room temperature and at a total current of 1 ampere, and with a plating time of ten minutes. Each glycolic compound was used in a plating solution containing no nickel, and again in a solution containing 0.02 gram per liter of nickel added in the form of nickel sulfate to the plating bath.

Table l Glycolic Compound Results Nickel Cone, Name Cone, g./l Brightness Bright Current Density g Area }Diethylene glycol monoethyl ether-- low and middle. middle and high.

Of the various glycolic compounds which may be used in accordance with the method of this invention, we have obtained particularly satisfactory results using butyl ether derivatives of ethylene glycol. Diethylene glycol monobutyl ether, for example, has been found to be a particularly effective brightener over a very wide current density range, and we therefore consider this compound to be especially suitable for commercial use in bright cadmium plating according to this invention. sults also are obtained, as indicated in Table I, when using diethylene glycol dibutyl ether, and when using ethylene glycol 2-ethyl butyl ether.

Our experience has indicated that any water-dispersible cellulose derivative may be used efiectively in bright cadmium plating baths prepared according to our invention.

Excellent re- }Diethylene glycol monobutyl ether. gg ggfi )Diethylene gylcol dibutyl ether E8: }Diethylene gylcol hexylether low middle middle y e e y c igg (132% m e }Dlethylene gylcol oveirglll, slime smut.

mi e }Triethylene glycol i all except 10w 10%. oy1ene g yc $551 g }Dipropylene glycol g }Methoxy propylene glycol gi: some haze middle 34. t xy t e yle e yc 2 overall some ham iEthylene glycol ethyl ether ig 3? }Ethylene glycol diethyl ethergagg }Ethylene glycol Z-ethyl butyl ether... %g

0. 1 10W 407 }Ethylcne glycol hexyl ether 24 133 23 Very 4 m e }Ethylene glycol butyl ether... 4 w and i }Ethy1ene glycol methyl ether. 6 $535 }Dlethylene glycol monovinyl ether. 1% g 0. 0 ow ibutoxy Tetra glycol 0. 04 overall, some haze. }Polyethylene glycol, av. mol. wt. 300.. 5 2; 1 0. 1 overall, some haze. Polyethylene glycol, av. mol. wt. 400.. 1 overall, slight ham }Polyethylene glycol, av. mol. wt. 600.- gg' }Polyethylene glycol, av. mol. wt. 1,000. i }Polyethylene glycol, av. mol. wt. 3,400. ggi gigg }Polyethy1ene glycol, av. mol. wt. 6,800. ifggg }Polyethylene glycol, av. mol. wt. 0. 01 upper pg.

20,000. Ob0i upper upper 0 }Polypropylene glycol, av. mol. wt. 400. $3, soome Streaks mi e }Tetraethy1ene glycol dimethyl ether... 4 middle and uppen Table II below summarizes a number of examples of the method of this invention in which difierent cellulose derivatives were used. The results of Table II were obtained by electroplating cadmium from a solution having the basic composition given above and to which 2 grams per liter of diethylene glycol monobutyl ether had been added. The cadmium was electroplated from the solution in a Hull test cell at a total current of 1 ampere and at room temperature. The various cellulose derivatives set forth in Table II were dispersed in the solution in the concentrations indicated. Each cellulose compound Was tested in a solution free from nickel, and again in a solution to which 0.02 gram per liter of nickel, added as nickel sulfate, had been dissolved.

Table II Cellulose Derivative Results Nickel Cone, Name Cone, g./1. Brightness Bright Current Density .[1 Area Hydroxyethyl cellulose 333% except lower 0.12 low and high. Garboxymethyl cellulose 0.12 overall, except very low. Carboxymethyl-hydroxyethyl cellulose- 38' 0.01 overall. Oxidized mums "i 0.12 0.02 Brilliant upper 54.

@SQQBBB.

It Will e t d m th f re oi ab e th exidized cellulose, when used in the solution containing no nickel and at the minimum preferred concentration, resulted in the electrodeposit being less bright than was the case in the other tests. However, when the concentration of the oxidized cellulose was increased to a value ell, With he P f r d n e n hen t w s u ed in the presence of dissolved nickel, it resulted in an excep tionally bright deposit in the higher current density range. Since performance of this material seems to be more dependent on concentration and on other factors than the first three compounds listed in Table II, it is relatively less satisfactory than the latter for commercial use.

The wide concentration range of the. glycolic compound and the wide current density range over which bright deposits can be obtained by the method of this invention is illustrated in Table III below. In carrying out the examples summarized in Table III, 0.1 gram per liter of hydroxyethyl cellulose and 0.02 gram per liter of nickel (added as nickel sulfate) were incorporated in an alkali cyanide cadmium solution of the basic composition stated above. Diethylene glycol mqnohntyl ether was added to the solution in the amounts indicated in the table, and cadmium was plated from the solution at room temperature, without agitation, on steel cathodes immersed in the bath.

T able I II Dicthylene Brightness of Cathode Deposit at Current Density of Glycol Monobutyl Ether Cone, g./l. Amps. per sq. ft.

25 Amps. per 40 Amps. per sq. ft. sq. ft.

Bright with smut.

Bright Bright. Bright, some smut. do Do. Dullish bright Very Bright... Very Bright. do do Bright. do Bright, Lack- Dullish Bright.

tug Full Luster.

Table III indicates that for optimum results the current density from 20 to 40 amperes per square foot should be used. In particular, low current densities of about 10 amperes per square foot or less give less satisfactory bright deposits than are obtained at the higher current densities. However, even at low current densities, a degree of brightening which is useful for many purposes can be obtained.

As shown in Table IV below, the concentration of the cellulose derivative, within the preferred range contemplated by the invention, and particularly in the presence of dissolved nickel, is not critical. In carrying out the examples summarized in Table IV, 2 grams per liter of diethylene glycol monobutyl ether were dissolved in an alkali cadmium cyanide solution having the basic composition stated above. Hydroxyethyl cellulose was dissolved in the resulting solution at concentrations indicated in Table IV, and nickel sulfate was also dissolved therein to yield the nickel concentrations indicated. Cadmium was electrodeposited from the resulting solution at room temperature, without agitation, on steel cathodes, and the character of the electrodeposit formed at various current densities was noted.

Table IV Hydroxyeth yl N i ekel Current Cellulose 00110., Density, Character of Deposit Cone, g./1. g./l. Amps. per

sq. ft.

0.01 0.02 25 to 40 Very Bright. 0.1 0.02 to 50 Brilliant. 0. 4 0. 02 25 and 40 Bright. 0.8 0. 02 10 to 40 Dullish Bright, some smut. 0.1 0.01 25 to 10 Bright. 0. l 0. 46 2'3 and 40 Bright at 25 a. s. f., some haze at 40 a. s. t.

We claim:

1. process for producing bright cadmium deposits,

whi h c mprises. el ctrodepositing cadmium fro a aqueous alkaline solution containing from 50 to' 150 grams Pe l e f an. li me a cy ni e, from It! to-5 grams per liter of cadmium, from ,4 to. gram per liter of a waten dispersible cellulose derivative, and from M to 30 ams pe it r. of a y oli ompound havi th f l in h h R is a s h the elect d fr m the ro wating of hydr e nd alkyl adical c nta nin from 1 t 6 r on a m X' s a ubst ent sele ed om the up s st n of y ogen, m hyl and ethy and n in which. R is. a subs ue t, selected from he g o p eon-v si ting f hyd ogen al yl a c n aining rom; 1 to 6 carbon atb ns, X is a s b e selected rom h group consisting of hydrogen, methyl, Alia" ethyL'and is a number from 0 to 500.

3. A process for producing bright cadmium deposits which comprises electrodepositing cadmium from an aqueous alkaline solution containing from 50 to 150 grams per liter of an alkali metal cyanide, from 10 to 50 grams per liter of cadmium, from 5 to gram per liter of nickel, from ,4 to gram per liter of a water-dispersible cellulose derivative, and from A to 30 grams per liter of a glycolic compound-having the formula in which R is a substituent selected from the group consisting of hydrogen and alkyl radicals containing from 1 to 6 carbon atoms, X is a substituent selected from the group consisting of hydrogen, methyl, and ethyl, and n is anumber from 0 to 500.

4. A process for producing bright cadmium deposits which comprises electrodepositing cadmium from an aqueous alkaline solution containing from 65 to grams per liter of an alkali metal cyanide, from 15 to 35 grams per liter of cadmium, from $5 to V2 gram per liter of nickel, from ,4 to /2 gram per liter of a Water-dispersible cellulose derivative, and from 1 to 4 grams per liter of a glycolic compound having the formula in which R is a substituent selected from the group consisting of hydrogen and alkyl radicals containing from 1 to 6 carbon atoms, X is a substituent selected from the group consisting of hydrogen, methyl, and ethyl, and n is a number from 0 to 500.

5. A process for producing bright cadmium deposits which comprises electrodepositing cadmium from an aqueous alkaline solution containing from 65 to 130 grams per liter of an alkali metal cyanide, from 15 to 35 grams per liter of cadmium, from 5 to gram per liter of a cellulose derivative selected from the group consisting of hydroxyethyl cellulose, carboxymethyl cellulose, and hydroxyethyl carboxymethyl cellulose, and from 1 to 4 grams per liter of an ether derivative of a compound selected from the group consisting of alkylene glycols and polyalkylene glycols.

6. A process for producing bright cadmium deposits which comprises electrodepositing cadmium from an aqueous alkaline solution containing from 65 to 130 grams per liter of an alkali metal cyanide, from 15 to 35 grams per liter of cadmium, from to /2 gram per liter of a cellulose derivative selected from the group consisting of hydroxyethyl cellulose, carboxymethyl cellulose, and hydroxyethyl carboxymethyl cellulose, and from 1 to 4 grams per liter of a compound selected from the group consisting of alkylene glycols and polyalkylene glycols.

7. A process for producing bright cadmium deposits which comprises electrodepositing cadmium from an aqueous alkaline solution containing from 65 to 130 grams per liter of an alkali metal cyanide, from 15 to 35 grams per liter of cadmium, from to /2 gram per liter of nickel, from 4 to h gram per liter of hydroxyethyl cellulose, and from 1 to 4 grams per liter of diethylene glycol butyl ether.

8. An aqueous alkali-cyanide cadmium plating bath containing from 50 to 150 grams per liter of an alkali metal cyanide, from to 50 grams per liter of cadmium, from M to gram per liter of a water-dispersible cellulose derivative, and from /4 to grams per liter of a glycolic compound having the formula in which R is a substituent selected from the group consisting of hydrogen and alkyl radicals containing from 1 to 6 carbon atoms, X is a substituent selected from the 8 group consisting of hydrogen, methyl, and ethyl, and n is a number from 0 to 500.

9. An aqueous alkali-cyanide cadmium plating bath containing from 65 to 130 grams per liter of an alkali metal cyanide, from 15 to grams per liter of cadmium, from to /2 gram per liter of nickel, from A to /2 gram per liter of a water-dispersible cellulose derivative, and from 1 to 4 grams per liter of a glycolic compound having the formula in which R is a substituent selected from the group consisting of hydrogen and alkyl radicals containing from 1 to 6 carbon atoms, X is a substituent selected from the group consisting of hydrogen, methyl, and ethyl, and n is a number from 0 to 500.

10. An aqueous alkali cyanide plating bath containing from to 130 grams per liter of an alkali metal cyanide, from 15 to 35 grams per liter of cadmium, from to /2 gram per liter of nickel, from 5 to /2 gram per liter of hydroxyethyl cellulose, and from 1 to 4 grams per liter of diethylene glycol butyl ether.

References Cited in the file of this patent UNITED STATES PATENTS 2,107,806 Solderberg et al. Feb. 8, 1938 2,526,999 Diggin et al Oct. 24, 1950 30 2,615,837 Liger Oct. 28, 1952 

1. A PROCESS FOR PRODUCING BRIGHT CADMIUM DEPOSITS WHICH COMPRISES ELECTRODEPOSITING CADMIUM FROM AN AQUEOUS ALKALINE SOLUTION CNTAINING FROM 50 TO 150 GRAMS PER LITER OF AN ALKALI METAL CYANIDE, FROM 10 TO 50 GRAMS PER LITER OF CADMIUM, FROM 1/1000 TO 3/4 GRAM PER LITER OF A WATER-DISPERSIBLE CELLULOSE DERIVATIVE, AND FROM 1/4 TO 30 GRAMS PER LITER OF A GLYCOLIC COMPOUND HAVING THE FORMULA 